Improved plasma operations in the DIII-D tokamak

Summary form only given. The DIII-D program has made substantial progress in recent years on a wide range of tokamak physics and technology issues. Two key elements of this progress has been the control of plasma-wall interactions and implementation of an advanced plasma control system. Boronization of the vacuum vessel along with careful attention to vacuum quality and the removal of wall impurities has led to a significant reduction in the oxygen and metal impurity levels in the plasma and to the discovery of a very high confinement mode (VH-mode) with exceptionally good energy confinement times exceeding L-mode by a factor 3.5. The boronization has also significantly reduced the recovery time from a vent. The advanced digital plasma control system allows rapid and reliable changeover from one plasma configuration to another. The system has already allowed the VH-mode to be extended to quasi-steady state by keeping the stored energy in the plasma constant by controlling the power of the injected neutral beams.